Scan apparatus



J. H. PRATT SCAN APPARATUS Oct. 13, 1953 2 Sheets-Sheet l Filed June ll,1951 Oct. 13,

Filed June l1, 1951 J. H. PRATT SCAN APPARATUS 2 Sheets-Sheet 2 I n l@if i BY hema,

ATTORNEY Patented Oct. 13, 1953 SCAN APPARATUS John H. Pratt, LaCrescenta, Calif., assigner to Radio Corporation of America, acorporation of Delaware Application June 11, 1951, Serial No. 230,957

The present invention is related to motor control apparatus and moreparticularly to positioning devices.

In radar (radio echo detection and ranging) systems, it is often desiredto scan a particular sector of space with a beam of pulsed radio energyfrom an antenna. Reilections of the energy by distant objects may thensupply an indication of position. The range measure is obtained bymeasuring the time for the pulse to travel to and return from the objectunder study. The angular position from the radar set may be obtained byknowledge of the direction in which the antenna is pointing at the timethe pulse was transmitted and received. The angular measure may berestricted to one plane, as the azimuthal plane, or one angle ofaltitude, or both of these angular directions, azimuth and altitude maybe desired and obtained.

It is often desirable, in radar systems, to scan predetermined sectorsconstant speed. incependent of wind and other forces. However, it is notusual to be able to select the angular width of the scanned sector to beany desired angle within specied limits of a range of sector sizessimply, and if desired, from a remote position. Such selection ifdesired has heretofore required additional equipment often prohibitiveby reason of expense, bulk of additional components required, and otherdesign diiiiculties. It is further desirable to select the center lineor mid-line of the sector to be scanned. This has heretofore beenaccomplished for predetermined sectors. However, there has been nosimple or convenient means heretofore known by which the centraldirection of the sector scan may be selected at will over a large sectorand also by which the size or angle of the sector may be selected atwill over a range of sector sizes.

It is also often desirable, in radar systems, to rotate the antennacontinuously at constant speed; the speed to be independent of windloading, variable frictional forces and other forces which might tend tovary the speed. This has not heretofore been done by simple orconvenient means when the function of the antenna control equipmentincluded controlling the position of the antenna.

Although the invention is herein described in connection with radarscanning, it will be apparent that it has other applications Where itmay be desired to oscillate equipment back and forth over a rangeselectable at will within limits, or to continuously move saidequipment, and also to select at will the median point or position ofthe oscillations.

It is an object of the invention to improve radar scanning control, andmore generally, the control of motors.

Another object of, the invention is to provide 10 Claims. (C1. S18-28)scan apparatus, whether for radar or for other purposes, of greaterflexibility in use and subject to greater control than those heretoforeavailable.

Still another object of the invention is to provide scan apparatus inwhich the sector to be scanned may be selected at will within limits andthe median or center of the sector may also be selected at will.

A still further object or the invention is to provide means to scan inthe manner just described in a comparatively compact and simpleapparatus.

Still another object of the invention is to provide improved apparatusfor continuously rotating or moving an object at a constant,closelycontrolled speed independent of varying forces tending tospeed-up or slow-down the rotational velocity, while the apparatus mayalso be used to position the object.

Another object of the invention is to provide an improved apparatus bywhich an object may be positioned at will, or alternatively caused toscan, and by which the scan sector, both in amplitude and direction, maybe selected at will.

According to one important feature of the invention, the same servosystem is operated as a position servo or a speed servo, by applying theposition voltage as the error signal of the servo system, or by applyinga speed error voltage. ln this fashion, there need be very fewcomponents added to an ordinary radar system, which usually has apositioning servo-system, to make available the advantageous featuresthe vention. Preferably the speed voltage from which the speed errorvoltage is derived, is employed to modify the position control voltagewhen the system is operated as a position servo system, to provide aproperly damped position control servo system.

According to another important feature of the invention, the scan motionis imparted to an object herein exemplified by a radar antenna, by aservo system operating as a speed servo, the error signal for which isthe diierence between the speed (or velocity) voltage and a speedcontrol voltage. Thus, the speed with which the scan motion occurs isreadily and advantageously controlled. The motion is reversed when theposition of the object to which the scan motion is to be impartedprovides a position voltage sufficient to operate a relay or reversingswitch by overcoming a reversal control voltage. Thus by selection ofthe reversal control voltage, the width or amplitude of the sector maybe selected at any desired Value. The position signal may be altered tohave a null stable position control value at any desired selected point,which determines the center or direction of the scanned sector. Byelimination of the control of the reversing relay by the positionvoltage the radar 3 antenna may be made to rotate continuously in onedirection.

The foregoing objects, advantages, and novel features of the inventionwill be more apparent from the following description when taken inconnection with the accompanying drawing, in which like parts have likereference numerals and in which:

Fig. 1 is a diagram schematically illustrating one embodiment of thepresent invention employing a gas tube reversing circuit; and

Fig. 2 is a diagram schematically illustrating a circuit which may beoptionally substituted for the gas tube reversing circuit of Fig. 1.

Referring to Fig. 1 an apparatus to be positioned and oscillated orscanned at will is the radar antenna l driven by a motor l2. A radartransmitter and receiver I4 is connected electrically in known manner tosupply information of the range of energy reflecting objects bymea-suring the time for the signal to travel from the antenna ID to theobjects and return. Information of the angle of the reflecting objectmay be indicated by the radar by correlating the angular position of theantenna HJ with the indicator, also in known manner.

The rotor i8 of a synchro-transformer i6 is mechanically connected totake a -position determined by the angular position of antenna I3. Therotor I8 is electrically connected to a source of A. C. power il, theterminals of which are schematically indicated as XY. To simplify thedescription, it may be assumed that the antenna i6 is driven in azimuthonly by the motor l2.

The stator windings 2G of the synchro-transformer 6 are connected to thestator windings 22 of a second synchro transformer 24. The control rotor2E of the second synchro transformer 24 is connected mechanically to ahand whe-el 23. The control rotor 26 is electrically connected toterminals IJ across which appears a position control voltage which hasan amplitude proportional to the displacement of the first rotor I8 (andantenna I6) from an angular position of correspondence with the positionof second rotor 26 controlled manually by the hand wheel. The positioncontrol Voltage across terminals IJ also is in or out of phase with thevoltage across terminals XY depending on the sense of the lack ofpositional correspondence of the first rotor 1,8 with that of the secondrotor 26.

A relay 30 has four sets of single poledouble throw contacts 30a, 30h,33C, and 33d, and a second relay 32 has four sets of single pole doublethrow contacts 32a, 32D, 32e, and 32d. A doublepole selector switch 34with sections 34a and 34h has three positions. In the position marked Mpower is applied from the source Il to the windings 36@ and 32erespectively of relays 33 and 32 through section 34a. When the selectorswitch 34 is in the position marked M, the relays 30 and 32 are actuatedto close the contacts 33a to 30d and 32a to 32d to the positiondesignated M. When selector 34 is in the positions designated SS or C,the relays 3G and 32 are restored to their normal position to close thecontacts 30a to 30d and 32a to 32d to the position designated SS. Thefunction of section 34h of switch 34 is to make circuit connectionsrequired to cause the operation of the antenna in continuous rotationand is described more fully hereinafter. rI`he position of the relays toclose the contacts designated M is selected for operation with manualcontrol. In this M position of selector switch 34, the antenna le is torespond to the position of the handwheel 28 to seek positionalcorrespondence therewith, but without scanning. In the SS position, thehandwheel 26 controls the position of the center of a sector of desiredwidth. rlhe manner of operation is explained more fully hereinafter. Aservo amplifier 36 is connected to apply power to motor l2 in a phasecorresponding to the in-or-out-of-phase signals voltage received at itsinput terminal 38 and with an amplitude corresponding to the amplitudeof the input signal.

The remainder of the circuit will first be clescribed with selectorswitch 34 in the M position and then described with switch 34 in the SSposition. Finally, the circuit will be described with switch 34 in the Cposition.

With switch 34 in the M position, the servo amplifier input terminal 38receives an error signal through contacts 32o in the M position from thetap 49 of a potentiometer 42. A position control voltage is applied toone terminal 42a of the resistor of potentiometer 42 through contacts32d and contacts 30h from terminal I. 'Ihe other terminal 42o of theresistor of potentiometer 42 is connected to a common ground conductorindicated by the conventional symbol. Terminal I (shown adjacentcontacts 3th) isthe same as the terminal I shown at the second synchrotransformer 24, the terminal being thus shown at two points on theschematic to avoid the necessity of drawing a long possibly confusingconnecting conductor. Terminal I is one terminal of the control rotor26. The other terminal J of the control rotor 26 (shown at synchrotransformer 24 and also at contacts 30d) is connected with relays 3U and32 in M position, through contacts 33d and contacts 32h to one terminal44a of a resistor 44 of potentiometer 4E, .the other terminal 44D ofwhich is grounded. The arm 48 of potentiometer 46 in this position ofthe switches is connected to an open contact of the set of con.- tacts32C. The terminal 44a of re istor 44 is a junction connected to oneterminal of a resistor capacitor filter network 50. The other terminalof filter network 50 is connected to the arm terminal 52 of a Vibrator54 employed as a chopper or modulator.

The arm 56 of chopper 54 makes contact alternately to contacts 58 and60, the latter contact being grounded. rIhe arm 56 is actuated syn.-chronously with the alternations of source Il by `a polarized relaywinding 62 connected to source l1. A resistor capacitor network 64allows ad.- justment of the voltage applied to winding 62 to the propervalue to operate the contacts of chopper 54 in phase with the sourcevoltage. The ungrounded contact l58 of chopper 54 is connected throughcontacts 30C in the M position to potentiometer arm 65 of potentiometerE3. A tachometer 'l2 has its terminals VW (shown adjacent topotentiometer 63 and also at tachometer 'l2 near antenna I6) connectedacross the potentiometer resistor l0. rl'he tachometer l2 may be adirect current generator mechanically connected to antenna l0 to have anoutput voltage proportional, in amplitude and polarity, to the angularspeed or velocity of the antenna El). In the M position of the switch,the terminal W grounded through contacts 32a. Capacitor 24 lters highfrequency components from the velocity feedback voltage picked up bypotentiometer arm 66.

The operation, with the control switch 34 inthe M position, is that ofan ordinary servo-mechanism radar system. The handwheel 24, which may becalibrated if desired, is set to point the antenna l0 in any desireddirection. If there is a discrepancy in the handwheel position and thatof antenna li), there is also a discrepancy in the positions of therotors I8, 26 which causes a position control voltage to appear atcontrol rotor 26 terminals IJ. The position control voltage at terminalsI and J is applied by switch contacts 30h, 32d, and switch contacts 30dand 32h respectively between the terminals 42a and 44a ofpotentiomreters 42 and t6 respectively. The Voltage between terminals42a and 42h has a reference to ground by Virtue of the groundconnections of terminals 42h and 64b. A portion of the voltage asreferred vto ground is taken off by the potentiometer arm -voltage ispicked up by arm Bt of potentiometer '68, passes through contacts 30o tochopper 5e,

where it is converted with the aid of filter 50 to a sinusoidal voltagehaving an amplitude dependent on the angular velocity of antenna l0(proportional to the driven speed of tachometer l2) and in or out ofphase with the voltage from A. C. source I1 depending on the directionin which antenna I0 is being driven (which. determines the polarity ofthe D. C. output at terminals VW). The converted sinusoidal velocityvoltage is added or subtracted from the error signal applied to inputterminal 38, and serves thereby as a rate or anticipatory voltageimproving the performance of the servo-system. As well understood, theerror voltage connections and that of the velocity feedback connectionsmust be made to secure the proper phasing. Under conditions in which theantenna l is driving toward the desired position of correspondence,

the error voltage unmodified by the velocity feedback voltage should bein that phase to cause antenna l0 to drive toward the desired positionalthough decreasing in amplitude. The velocity feedback voltage shouldbe in the opposite phase,

`under these conditions.

With selector switch 34 in the SS position, the relays 3i) and 32 havetheir various contacts 33a to 30d and 32a to 32d in the positionsdesignated SS. Terminal 38 is then connected through contacts 32e to thepotentiometer arm 48. Contact Ma, is open circuited at contacts 32h butremains connected through filter 58 to the chopper terminal 52. Choppercontact 60 remains grounded but chopper contact 59 is connected bycontacts 30e through a resistor capacitor lter network 'i5 to thepotentiometer arm 16 of a potentiometer 18. The tachometer potentiometerarm B6 is left disconnected by contacts Sile in the SS position. Thepotentiometer resistor $0 is connected across the secondary 82 of atransformer M. The pri"- mary 86 of transformer is connected byterminals ZZ (shown also near motor I2) across the commutating fieldwinding t8 of motor l2. rihe commutating held winding is connected inseries with the armature of motor i2 in the usual manner. A ltercapacitor 90 is inserted across seoondary 84 to minimize passage ofcommutator sparking and other high-frequency voltages.

reversing relay potentiometer resistor |06.

Oney terminal of the secondary 82 is connected to the tachometerterminal V. The other tachometer terminal XW is connected by contacts32a to arm 92 of a speed control potentiometer 94. The speed controlpotentiometer resistor 98 has one terminal grounded and the other termi--nal connected to receive voltage from reversing relay contact arm |90.Capacitor S is connected between speed control potentiometer arm 92 andground. The arm It@ under sector scan control is to be switchedalternately from one to the other of contacts m2 and contact lcd in amanner to be described. rihe reversing relay contacts |02 and H24 areconnected across the resistor |36 of a potentiometer IGS. A directcurrent voltage supply H9 indicated schematically by a conventionalbattery syinbol is also connected across The arm ||2 of the reversingvoltage potentiometer I is grounded, so that the voltages at contactsHB2 and IEM may be adjusted to be equal in value but opposite inpolarity with respect to the ground conductor. Such adjustment isordinarily desired, as will appear hereinafter.

The reversing relay contact arm itil is actuated by relay |36, which ispart of a circuit designated as the reversing relay circuit Ehi. Thiscircuit includes first and second gas tubes HG and H8, each of which maybe of the type 2D21 thyratrons. Tubes HQ, HS have, respectively,cathodes EN), |22, control grids ld, |2, screen grids 28, i3d, andanodes E32, |34. rEhe rst gas tube anode |32, is connected through thewinding of relay |36 to one terminal lta of the secondary |38, centertap grounded, of a power transformer his. The second gas tube anode |34is connected through the winding lili of a relay Mii to the otherterminal lb of the power transformer secondary |38. The primary Edt ofthe power transformer ili receives voltage from the source Il'. The gastube cathodes are grounded. The gas tube screen grids |28 and |39 areconnected to a potentiometer resistor network |43, with the second tubescreen grid e connected to a junction between one terminal of each oftwo equal resistors |55 and I 52. li potentiometer resistor |54 of apotentiometer |55 equal in value to the sum of the values of the seriesconnected resistors |59, |52 is shunted across their other terminals.The arm |55 of the shunted potentiometer IES is connected to the rsttube screen grid |253. One terminal of a resistor Ico is connected tothe Junction of the netwerk potentiometer resistor |54. The otherterminal of resistor |50 is connected at a junction point |52 to thenegative terminal of a direct current voltage source iii-e, the positiveterminal. of which is grounded.

A sector width control potentiometer it has its resistor iti! connectedbetween the junction |52 and ground, and has its arm ilo connected toapply voltage through contacts Scrl in the SS' position between terminalJ of the position ccntrol synchro rotor 2d and ground. Relay i3 has twosets of contacts, those already described as the reversing relaycontacts H32 and Itri, and a second set of contacts It? and mi?. Ti esecond set of contacts are made by contact arm |12, normally connectedto contact it?, and actuated by current through the winding of relay i33 to make contact |69 and break contact itil. rEhe arm il? is connectedthrough a current-limiting resistor |14 to the iirst tube control gridim. The contact ll is connected through a current-limiting resistor |'i6to the second tube control grid |23. Relay |42 in the second tube anodecircuit has a ,lys/55,528

contact arm |18 and a contact |80 connected in the rst tube anodecircuit between relay wind.- ing |36 and the power transformer primaryter.- mina-l |3Ba. The arm |18 is normally closed to contact |80 tocomplete or make the rst tube anode circuit when no current passesthrough the winding |42 of relay |.44 and is opened to interrupt orbreak the rst tube anode circuit when current passes through the Winding|42. Power transformer terminal |3.8b is connected through a resistor|82 through contacts 30a in the SS position to ground, and in the Mposition to contact |01 of the relay |36.

In operation, when the selector switch 34 is in the SS position, theservo ampliiier input terl for optimum operation. The junction 44a re.-

ceives voltage from the chopper 54 through the filter 50. The choppercontact 53 receives its voltage through contacts 32o in the SS positionfrom potentiometer arm 1.6 which picks off the potentiometer a voltatgederived from .the field winding 8S of the .drive motor |2. This voltagepicked up by the arm 1.5, adjustable to opti.- mum values, is, becauseof the connection of transformer 84, proportional to the rate of changeof current through eld Winding 88; the secondary voltage beingproportional to the rate of change of the primary current. Since theprimary current is proportional to the current through (and voltageacross) the field Winding 08,

the voltage picked up by the arm I8 is propor.- f

tional to the rate of change of speed of the motor |2 and or the antennaI0.

The rate of change of speed voltage is serially connected with thetachoineter voltage through terminals V and W, and through contacts 32ain the SS position with a vdirect current (D. C.) voltage picked up atarm 02 of the speed control potentiometer 94. The D. C. speed controlvoltage is positive or negative with respect .to ground `depending onwhich of relay contacts |02 and |04 is made at the time, but preferablyis the same in magnitude whether positive or negative, due to adjustmentof the speed balance control ||2, to make the scanning speed in eitherdirection across the sector the same.

The voltages thus applied. to the input terminal of the servo amplifier(before chopping), include rst, a voltage proportional to the rate ofchange of velocity of antenna I9., second a voltage proportional to thevelocity of antenna I0, and third a D. C. velocity or speed controlvoltage, all serially connected and therefore each being respectivelyadded or subtracted. The polarities of the connections are selected forthe second voltage (the velocity or speed voltage) so that the motordrives at a velocity and in a direction to reduce this speed voltage.The speed control voltage added to this speed voltage causes the motorand antenna to drive at a speed and in a direction to equalize the twovoltages, the direction of drive therefore being determined by thepolarity of the speed control voltage, and tend.- ing to remainconstant. The rate of change of speed voltage is added to stabilize andincrease the speed constancy. Its polarity is selected so that, when theantenna drive speed is increasing toward a constant speed, the rate ofchange of speed voltage tends to decrase the speed of drive.

Turning attention to the reversing relay circuit; voltage freni theposition control rotor 2.6

is impressed by contacts 30h and 30d between the contact |06 and the SSwidth control potentiometer arm |10.. This introduces an A, C. voltagein or out of phase with source I1 in series with the D. C. voltage fromsource |64, which is impressed on both of the control grids |24 and |26.The amplitude of this A. C. voltage depends on the positionalcorrespondence between the antenna and the handwheel 28.

The cyclical operation caused by the reversing relay circuit may beexamined starting from correspondence between the handwheel 23 and theantenna, when the amplitude of the A. C. voltages supplied to the tubecontrol grids |24 and |26 are zero. With the selector switch 34 in theSS position both tubes are nonconductive, due to the bias from D. C.VSource |04 on the screen grids. The antenna is now driving in onedirection. The connections are made in such a polar.- ity that anincreasing A. C. voltage derived from the position control rotor 2 6 isapplied to the control grids |24 and |28 in phase with the voltage fromterminal |3,Sa of the power transformer. When the antenna has drivensuhciently far so that the A. C. voltage overcomes the bias, the rsttube ||6 is caused .t0 Conduct. Reversing relay |36 is actuated, causingcontact 1 04 to break and contact |02 to make, thereby reversing thedirection of drive.

The antenna now quickly reverses and drives at a. constant speeddetermined by the speed .control voltage in the opposite direction.Actuation of reversing relay |36 also causes contact L31 to break andcontact |09 to make. From contact |09, the first tube control gridreceives a voltage from power transformer terminal |38@ in phase withits anode voltage (through a resistor) which keeps the first tube IISconducting. The reversing relay thus remains actuated as the antennadrives toward and past the position of correspondence with the handwheel28. As the antenna passes the position of correspondence with handwheel2B. the A C. voltage from control rotor 25 applied to contact |01 andthe eccnd tube grid |26 reverses phase, after becomins zero inamplitude, and increases in amplitude and remains then yin phase withthe voltase .at terminal ISBD. When the antenna reaches a certainpositiefsV the voltage at .the sec- 0nd tube control grid .is Suiicientto .Cause tube H18 to conduct, relay |44 is actuated to .Open the iirsttube anode circuit at Contact |80. The reversns relay contacts .returnto their vnormal positions, with contact |304 made and Contact |02 open;and contact |01 rnade and .contact |09 Open. The Speed .Control voltageis reversed, causing the antenna |53 quickly to reverse direction .anddrive .at Constant speed toward the position of correspondence withhandwheel 28. Shortly after this return drive begins, tube ||8 ceases toconduct, and relay contact |80 is again made. But tube H5 is nnt redagain until the antenna drives past positional correspondence withhandwheel 20 so that .the voltage at the first tube .control grid |23again fires tube HS.

With the .Selector switch 34 in the SS position and the reversing relaycircuit and speed balance properly adjusted, the antenna can `be made toscan over a sector centered on the position of correspondence with thehandwheel 28. The speed balance provides means for securing equalvelocity scan in each direction. The Width .of this sector may becalibrated closely to the position of the SS width control potentiometer|10, which may be calibrated for desired sector scan widths,

With the SS width control arm at ground, the minimum scan sector issecured. This may be made practically zero sector, so that the reversingrelay |3IJ` chatters rapidly, its contacts |02 and |04 being made atshort intervals. In this condition, when there is positionalcorrespondence of the antenna with handwheel 28, inertia of the systemis sufficiently great so that the antenna I0 can actually be positionedby the handwheel 28 almost as well as when the selector switch is in Mposition, although positioning is not as smoothly accomplished and notas accurate, the system having some degree of overshoot. At the otherextreme, with the SS width control arm |70 arranged to pick up voltagenear the junction of resistors |83 and |08 the sector width is nearly180. The voltage across potentiometer |68 is limited to a value lessthan that required to produce a scan width of 180. If the voltage weregreater than this the antenna would rotate continuously in one directionbecause the voltage from the control rotor 2S would always beinsufficient to cause conduction of tubes I5 or IIB and relay arm |00would remain in one position or the other. The capacitors connectedacross the relay ywindings |35 and |42 are to prevent chattering,because the tubes I I6, I8 actually conduct only on half cycles of thepower transformer voltage.

Position C of selector switch 34 is provided to produce continuousrotation when this is required. In this position maximum negativevoltage is applied to the grids of tubes IIE and IIB and they remain cutoff. Switch 34 might be turned to the C position from the SS positionwhen tube I|6 was locked on through contact |00 of relay |36. Thus, ifother means were not provided, the antenna. might rotate in eitherdirection when switch 34 was placed in the C' position. Because it maybe desirable that the antenna always rotate in the same direction acircuit is provided to ensure this. In passing through the M position ofswitch 34 on the way to the C position resistor |02 is connected,through the M contact of relay contact 30a to contact and junction |06and the grid of tube I I8. This places a voltage on the grid |28 of tubeH0 in phase with the plate voltage and the tube iires. operating relay|42 and opening contact |80 in the plate circuit of tube IIS. If tubeIIS is locked on, the locking circuit is broken by this action and thetube H6 ceases to re since the voltage applied to its grid throughcontact |06 is out of phase with its plate voltage. As switch 34 ismoved on to the C position a high negative D. C. voltage is applied toboth tube grids from junction point |62 and both tubes are thereby cutoil. rIhus it is always assured that both tubes are cut off in the Cposition, contact |04 is always made, and the antenna always rotates inthe same direction.

The details of the servo amplifier have not been illustrated. Varioussuitable amplifiers are known. The one actually employed applies powerfrom a three phase source through gas tubes to the D. C. motor I2 and isa known circuit with only minor variations. The D. C. voltage supplieshave been illustrated as batteries, although the usual rectifier powersupplies are employed.

These simplifications enable illustration of the F invention without itsobscuration by circuit details which are readily supplied by personsskilled in the art. Sufficient detail, however, has been shown to enableone skilled in the art readily to make a practical circuit, usable inthe eld.

flexibility, same servo amplier is employed to serve as Many variationsof the invention are possible. For example, it is apparent that a D. C.servo amplifier could be employed by suitable variations of thecircuitry. As a specic example of one variation, the reversing relaycircuit I I4 may be replaced by the circuit of Fig. 2. In Fig. 2, thecontacts 30h and 30e of Fig. l are shown. The contacts 30a need not beemployed. In the SS position of relay 30, voltage from the control rotor2S is applied to a phase detector and ampliner 200. This voltage iscompared with the phase or a voltage from a transformer 202 suppliedwith power from .source |71. When the voltage from terminals I to J isin one phase, the output at terminal 204 of the detector and amplifier200 is one polarity, and a reverse polarity when the voltage fromterminals I to J is in the reverse polarity. The amplitude of the outputvoltage at terminal 204 is proportional to the amplitude of the voltagefrom terminals I to J. The output from terminal 204 is applied to thewinding 200 of a polarized relay 208. The winding 205 is also seriallyconnected through arm 2 I0 to either one or the other of contacts 2|2 or2M of reversible relay 208. The voltages at terminals 2I2, 2 I4 areequal and of opposite polarity. The relay 208 also operates to connectterminal |00 with alternate ones of contacts |02 and |04 on eachreversal, as illustrated.

The voltage at terminal 204 must overcome that at a contact 2 I2 tocause the relay to operate in one direction; and that at 204 mustovercome that at contact 2I4 to cause the relay to operate in the otherdirection. Therefore, since the output at terminal 204 is proportionalin amplitude to the departure from positional correspondence of antenna.I0 from handwheel 28, it is clear that with the proper polarity andphase connections, the desired sequential reversals or" connections tocontacts |02 and |04 is secured. The operation with this variation isnow clear from what was previously described for the SS position ofselector switch 34. Operation in the M position of the selector switch34 is unchanged. Operation for switch 34 in the C position forcontinuous scan can also be secured if desired by having section 34happly a fixed voltage of desired amplitude as a speed control voltage,as shown.

In summary, with the selector switch 34 closed in M position, theservo-system for positioning the antenna I0 is operated as a positionservo. The servo ampliiier then receives as an error signal a positionalcontrol voltage proportional to the lack of positional correspondencebetween the handwheel 28 and the antenna I0, and with a suitable ratesignal introduced to improve the system stability. With the selectorswitch 34 in SS position, the same servo amplifier receives as errorsignal the diiierence between a speed voltage and a reversible polarityspeed control voltage, the latter being reversed by a circuit responsiveto the position control voltage reaching an arbitrarily selectedamplitude, and with a suitable rate of change of speed signal introducedto improve the stability (constancy of speed) of the speed servo system.With the selector switch in the C position operation is the same as inthe SS position except that the speed control voltage is unidirectionaland iiXed in amplitude and the antenna rotates continuously at constantspeed.

It is apparent that the invention provides an especially useful type ofmotor control, having and comparative simplicity. The

position servo amplifier, a reversible sector-scan speed amplifier, or acontinuous scan speed amplier. Scanning in both elevation and azimuthmay be secured by duplicating the system shown with an elevation scanmotor, except, of course, that scanning in elevation is limited. In thisevent (a) the antenna i may be fiXedly positioned in either elevation orazimuth under handwheel control; (b) the antenna Iii may be xedlypositioned at a selected point in one of these coordinates, and scannedabout a selected value over a selected sector of the other coordinate;(c) the antenna I il may be scanned about selected points with selectedsector angles, oliferent if desired, in both coordinates; (d) theantenna lil may be scanned continuously in one coordinate, e. g.azimuth, and scanned over a selected sector angle about a selected anglein the other coordinate. It should be noted that the scanning motionsare at substantially constant speeds, excepting of course at the time ofreversa-l of directions. This is often a desirable characteristic, as isunderstood in the radar art.

What is claimed is:

l. A servo system comprising a servo ampliiier having an input circuitand having an output circuit responsive to the sense and amplitude ofvoltage applied to said input circuit, a motor connected to receive theamplifier output and responsive thereto, an object driven by said motor,a position control element, means to derive a position control voltagehaving a sense and an plitude corresponding to the lack of positionalcorrespondence between said object and saidv control element, means toderive a speed voltage having sense and amplitude corresponding to thespeed of said object, means supplying a speed control voltage, andswitch means selectively applying one of said positional control voltageand the difference between said speed voltage and speed control voltageto said amplifier input circuit whereby the system operates' accordinglyas one of a positioning servo system and a speed servo system.

2. A servo system comprisingV a servo amplifier having an input andhaving an output responsive to the sense and amplitude of voltageapplied to said input, a reversible motor connected to receive theampliner output and responsive thereto, an object d'iven by said motor,a position control element, means to derive a position control voltagehaving a sense and amplitude corresponding to the lack of positionalcorrespondence between said object and said control element, means toderive a speed voltage having sense and amplitude corresponding to thespeed ol said object, means supplying a speed control voltage, andswitch means selectively applying to said input said positional controlvoltage modified by said speed Voltage, and a diierence voltage betweensaid speed and speed' control voltages.

3. The system claimed in claim 2 further comprising means to derive arate of changeof speed voltage, said diierence voltage being modied bysaid rate of change of speed voltage.

4. A servo system comprising a servo amplifier having an input andhaving an output responsive to the sense and amplitude of voltageapplied to said input, a reversible motor connected to receive theamplifier output and responsive thereto, an object driven by said motorya position control element, means to derive a position control voltagehaving a sense andV amplitude corresponding to the lack of positionalcorrellJ spondence between said object and said control element, meansto derive a speed voltage having sense and amplitude corresponding tothe speed of said object, a reversing means responsive to a reversalvoltage applied thereto to supply a rst speed control voltage of onesense when said reversal voltage has one amplitude and a rst sense andsupplying a second speed control voltage of sense opposite the nrst whensaid reversal voltage has another amplitude and a sense opposite that ofsaid rst reversal voltage sense, and switch means selectively applyingto said ampliiier input one of said positional control voltage and the.difference between said speed voltage and one of said speed controlvoltages supplied by said reversing means, said switch means alsoapplying to said reversal means as reversal voltage said positionalcontrol voltage during application to said amplifier of said differencevoltage.

5. The system claimed in claim 4, further comprising means to derive arate of change of speed voltage, and means to modify said speed voltageby said rate of change of speed voltage during application of saiddifference voltage to said amplier.

6. The system claimed in claim l', said means to derive a speed controlVoltage comprising a tachometer having a direct current voltage output.

7. The system claimed in claim 1, said position control voltage being analternating current voltage, one sense thereof being in phase and theother sense thereof being out of phase with respect to a referencevoltage.

8. The system claimed in claim 4, said switch means comprising a pair ofgas tubes each having an anode, cathode, and a control electrode, andconnected in circuit with one of` said tubes being conductive to drawcurrent exclusively of the other, a relay having a winding and a singlepole double throw switch actuated by current flow through said winding,said winding being connectedv in the anode circuit of one of said tubes,and a source supplying a directl current voltage, said position controlvoltage being added to said direct current voltage and appliedselectively to one of said control electrodes depending7 on which ofsaid tubes last became conductive.

9. The system claimed in claim 4, said reversing means comprising asecond switch means, a polarized relay actuating said second switchmeans and having a winding, a. direct current source in series with saidrelay winding in a polarity reversed by said second switch means, areference Voltage source, a phase detector having applied at its inputas said reversal voltage said positional control voltage, said referencevoltage source being connected to said detector, said detector having anoutput of direct current voltage of one polarity for voltage of onephase at its input and of the opposite polarity for voltage of theopposite phase at its input with reference to said reference voltage,the output amplitude being proportional to the input reversal voltageamplitude.

l0. The system claimed in claim 9, said position control voltage meanscomprising a pair of synchrotransformers, each having a rotor and astator, one rotor being mechanically connected to said object and theother rotor being connected to said reference voltage source, saidstator windings being connected together.

JOHN H. PRATT.

No references cited.

